Kate Fletcher is a folk musician who often accompanies songs and ballads with riffs / ostinato patterns on a very small number of strings on a lyre, kantele, or small harp. For an example, watch the final seconds of this video on youtube (around 2:45) where Kate is singing an English ballad while plucking an ostinato pattern on a Novgorod gusli. For another example of a different ballad with an ostinato pattern, this time played on a horsehair kantele, watch this video on youtube (at ca. 2:00).
For more information about Kate Fletcher, click here.
At the Nordic Harp Meeting 2016, Kate Fletcher taught together with Chris Foster some ballads that exist both in England and Scandinavia.